There are many applications where a fluid sample is to be tested for certain physical characteristics (such as electrical conductivity), or the presence of certain chemical or biological species (analytes). Such testing methods may involve a chemical reaction which can take some time to complete before the result is available to be read. The result can be read with a variety of methods such as electrical conductivity, optical density at a certain wavelength of light spectrophotometric), detection of presence of a color, fluorescence, luminescence, or a biosensor. Such applications include pollution monitoring and testing of salinity of drinking water. Another important area of application is the testing of a sample of biological fluid.
Diagnosis of many clinical conditions requires the detection of small quantities of specific chemicals in the person's body. In-vitro diagnostic devices (IVDs) are used to perform tests on samples such as urine, blood, saliva, or other body fluids. Most in vitro diagnostic tests are performed in the central laboratory of a hospital, and often by large expensive machines designed for batch processing of large numbers of samples which may require a panel of a number of tests. The results of the analysis are generally made available via the Laboratory Information System (LIS) to the hospital computer system for access by physicians at many sites throughout the hospital or clinic.
There are some clinical conditions where the central laboratory style of IVD testing often can not satisfy the need, either because of convenience or requirement for immediate results. In response to this clinical and market need, several companies have developed devices for portable, or near patient or so called Point of Care (POC) in vitro diagnostic tests. The instrument size and complexity depends on the application, from bench top to small enough to be worn in a shirt pocket.
For example, there are several companies today which provide small, battery powered, portable hand held instruments for testing of glucose in blood or urine. The availability of these devices has been a boon to diabetics who need to frequently test for blood glucose levels. These devices often consist of a small battery powered console, and a disposable test strip or cartridge. The fluid sample is placed into an aperture or onto a marked place on the test strip, and then the strip is placed into a reader, which reads some parameter of the chemicals to provide a quantitative (i.e.: numerical) or qualitative result. See, for example, the device described by Anderson et al in U.S. Pat. No. 5,279,294 Medical Diagnostic System, which uses a disposable lancet and reagent unit with a small battery powered portable instrument for measuring blood glucose. A similar device is described by Garcia et al in U.S. Pat. No. 4,787,398, Glucose Medical Monitoring System.
Another application where the central laboratory style of testing has limitations is in detection of acute myocardial infarct (AMI or heart attack) in patients who present to a hospital emergency room with chest pain. The current state of the art is to immediately test for a panel of cardiac related biochemical markers, which individually and in combination, can reveal the presence of an AMI. The most commonly used cardiac markers are Myoglobin, creatine kinase in its muscle/brain isoform (CK-MB), and Troponin.
The cardiac panel can be performed on serum or plasma (i.e.: blood from which the red blood cells have been removed), or on whole blood. There is an advantage in performing the tests on whole blood because it avoids the step of centrifuging blood to generate serum or plasma, and therefore may save vital minutes to a definitive diagnosis and allow earlier therapy delivery.
Most POC IVDs employ a variation on the same theme. An instrument is used to "read" the results from a disposable cartridge into which a small volume of sample has been placed. Larger instruments frequently can be connected to the LIS, whereas smaller ones often lack this feature.
Technologies to perform the reading include traditional chemistry such as spectrophotometry, biosensors (where the electrical properties of a sensor are affected by the presence of the analyte--see, for example, Ribi et al U.S. Pat. No. 5,491,097, Analyte Detection with Multilayered Bioelectronic Conductivity Sensors), immunofluorescence and immunoluminescence, to name a few. The techniques for managing fluid flow between the fluid sample and the reagents are well explored in a disposable device--see, for example, the work of Cathey et al as described in U.S. Pat. No. 5,660,993, Disposable Device in Diagnostic Assays.
In many of these systems, the chemistry system reacts with the analyte in the fluid sample, and an optically active marker chemical is excited with a laser at a particular wavelength, and then fluoresces at a different wavelength which is detected by a photodetector such as a photodiode or photomultiplier. Such instruments are made, for example, by Biosite Inc. (San Diego), or First Medical (Mountain View, Calif.). Another technology is surface plasmon resonance used in devices made by Quantech, Inc. (Minneapolis, Minn.).
The pressure for continuing miniaturization and reduction in cost is relentless. Electronic microcircuit fabrication technologies have been pressed into service to make sensor systems for multiple analytes, on a single chip, such as described by Hollis et al in U.S. Pat. No. 5,653,939, Optical and Electrical Methods and Apparatus for Molecule Detection. In recent years, electronic technology has progressed to the point where it has become feasible to manufacture at reasonable cost a complete disposable testing device which contains the chemicals necessary to do the test, as well as the optical and electronic components to read and display the result, and communicate the information to a hospital information system. Such a device is described in U.S. Pat. No. 5,279,294 Medical Diagnostic System by Anderson et al.
Although this device (manufactured and marketed by Metrika Inc, Mountain View, Calif.) and others like it represent a potential tremendous advance, it suffers from some serious limitations. Firstly, the power for the device is provided by small batteries similar to those used in a camera or a watch. These batteries add cost, weight, and reliability problems, as well as presenting a disposable hazard because of the toxic chemicals such as mercury and cadmium often used in the battery.
Furthermore, communication with the hospital information system or laboratory information system (LIS) is done by an electrical connector on the side of the printed circuit board (PCB) inside the device which mates with a connector on a reader or console which is connected to the LIS. A direct electrical connection requires an aperture to be made into the side of the device, complicating the internal design and adding size, weight and cost (the connector must be gold plated to facilitate reliable connection). Also, a direct electrical connection requires precise registration with the reader, which can be difficult and is fraught with reliability issues. Finally, in a laboratory environment with the presence of various types of fluids and chemicals, the connector on the reader or console could be subject to corrosion and degradation, again leading to poor reliability. Despite these limitations, direct electrical connection is the state of the art and is used in many instruments such as the one described by Holmes and Anderson in U.S. Pat. No. 5,371,687 Glucose Test Data Acquisition and Management System.
The present invention overcomes these limitations, and thereby improve the concept of a disposable self powered in vitro diagnostic device. The methods described are not limited to devices for performing in vitro diagnostic tests, and can be used for any device which operates with a fluid sample, for example, a self powered device for monitoring water pollution.